1. Technical Field of the Invention
The invention relates to a device for indicating that a reinforcing material, which is made of fibers and included in a composite material and which does not become translucent or transparent in wetting, has become wetted throughout by the matrix of the composite material while making the composite material. The device can indicate, for instance, that the carbon fiber reinforcement for the material of a hull or the like has been completely wetted throughout by liquid thermosetting plastic in the manufacture of the hull.
2. Description of the Related Art
An object of a composite material can be made by the material, which contains a reinforcement and a matrix that is liquid at certain stages of the manufacture, being supplied to a mould where the object obtains its shape when the matrix sets. Depending on whether the mould is of the type having a cavity or only a surface determining the shape of the object, the shape will be substantially determined by all its surface portions or only the inside or outside of the object. When manufacturing e.g. hulls of reinforced thermosetting plastic, moulds determining only the outer surface of the hull, so-called female moulds, are used in most cases.
One technique of manufacturing hulls is laminating by hand lay-up. The fibre reinforcement consisting of cut-out parts of a fabric or mat is arranged on a layer of liquid plastic which has been rolled on with a roller onto the mould surface. The reinforcement is then worked with a soft roller or brush so as to be impregnated and wetted with plastic. Finally, air and excess plastic are pressed out by means of a metal roller from the layer and the space between the layer and the underlying surface. Moreover, minor inclusions of air that are bound to the surfaces of the reinforcing fibres are removed. Owing to such working, wetting is further improved. The entire surface of each fiber of the reinforcement will then be substantially completely coated with matrix material.
To this first layer, additional layers are applied, as described above for the first layer. For large objects, use can be made of intermediate curings when making the laminate. Otherwise, all the layers can be applied in succession, curing taking place after application of the last layer.
After the application of each layer, it is necessary to make sure that the reinforcement of the layer has been properly wetted throughout. If the composite material should contain inclusions of air or voids, the hull will have an inferior quality with a risk of inferior strength since the composite can delaminate adjacent the inclusions of air and water can diffuse in the inclusions and cause chemical degradation of the material and cracking by frost. Insufficient wetting also reduces the resistance to compression of the composite, which may cause breaking of the hull.
For high-strength composite materials, a reinforcement consisting of practically merely carbon fibres or aramide fibers or a mixture thereof has recently come into use. The drawback of these materials is that it is difficult to visually form an opinion whether they have become well wetted throughout. To make sure that the wetting has been sufficient, ultrasonic testing and other testing techniques have been applied, which has contributed much to these composites being very expensive. The fact that the manufacture must be particularly precise owing to the lack of easy checking has also contributed to the increased cost.